The field of the invention relates to computer tomography and more particularly to image processing as it relates to computer tomography.
Conventional computer tomography (CT) machines use pixel-driven algorithms to reconstruct images for fan-beam x-ray sources. The conventional pixel-driven (CPD) approach normally is adapted to scan through each pixel location in raster-scan fashion, and find the angle of the ray that passes through each pixel grid for each view (snapshot). From the angle, a pair of corresponding ray numbers adjacent to the underlying pixel are determined. The pixel is then updated by adding a new value interpolated from the corresponding ray data. In a pipeline implementation, this type of backprojection module requires (1) an arc-tangent function, which may be implemented with a 2K by 32 bit table, (2) a full-size projection data buffer (2K by 32 bits), and (3) two reciprocal tables (each having a size of 4K by 16 bits). Because of the necessity of accommodating a wide variety of reconstruction geometries and field of views (FOVs), these tables are typically implemented in high speed static RAM (SRAM). The use of these full-size SRAM tables become a bottleneck to further reducing the hardware complexity in a parallel or pipeline processing environment.
Various efforts have been attempted in the past to try to simplify the CPD approach so that the backprojection and forward projection computations could be implemented in VLSI systems. Recent efforts have included an attempt to design a VLSI chip capable of reconstructing a 12-bit 1024 by 1024 pixel image from 1024 views. While these efforts have increased the speed of CT computations by using multiple VLSI processing units, none of these efforts have resulted in the maintenance of high image quality. On the contrary, some of these improvements have been made at the expense of good image quality. Because of the importance of CT, a need exists for improved methods and apparatus for simplifying the processing complexity of CT.